The present invention relates to an oil pump rotor used in an oil pump which intakes and expels a fluid according to changes in the capacity of a plurality of cells which are formed between inner and outer rotors.
Conventional oil pump rotors are provided with an inner rotor on which n (n being a natural number) outer teeth are formed, an outer rotor on which n+1 inner teeth are formed for engaging with the outer teeth, and a casing in which an intake port for taking in fluid and an expulsion port for expelling fluid are formed. In this oil pump, the inner rotor is rotated, causing the outer teeth to engage the inner teeth and thereby rotate the outer rotor. Fluid is then taken in or expelled due to changes in the capacity of the plurality of cells which are formed between the rotors.
Individual cells are partitioned due to contact between the respective outer teeth of the inner rotor and the inner teeth of the outer rotor at the front and rear of the direction of rotation, and by the presence of the casing of the oil pump which exactly covers either side of the inner and outer rotors. Thus, independent fluid carrier chambers are formed as a result. Once the capacity of a cell has fallen to a minimum value during the process of engagement between the outer teeth of the inner rotor and inner teeth of the outer rotor, the cell next proceeds along an intake port where its capacity is expanded, causing fluid to be taken in. After the cell's capacity reaches a maximum value, the cell next proceeds along an expulsion port where its capacity is decreased, causing the fluid to be expelled.
In this type of oil pump rotor, a sliding contact is always present between the casing and each edge surface of the inner and outer rotors, and between the outer periphery of the outer rotor and the casing. Further, a sliding contact is also always present between the outer teeth of the inner rotor and the inner teeth of the outer rotor at the front and rear of each cell. While this is extremely important for maintaining the liquid-tight character of the cells which are carrying the fluid, when the resistance generated by each of the sliding parts becomes large, then this sliding contact may cause a significant increase in mechanical loss in the oil pump. Accordingly, reducing the resistance generated by the various sliding parts in an oil pump has been a problem in this field.